Three dimensional measurement systems are being increasingly employed for vision systems in industrial environments. The environments often produce interference phenomena that reduce the ability of the vision system to make the needed measurements. Welding arc glare and other ambient light adversely affect vision systems sensitive to light of similar wavelengths. Much of the problem stems from using sensing devices that are exposed to the interfering light for more time than is absolutely necessary.
A measurement can only be made, by optical triangulation systems that project light patterns, when the projected light can be detected against any background light that is present. As the background light increases, the projected light intensity must be increased or some means of reducing the background light received by the reflected light sensor must be devised. By concentrating all the projected energy into a narrow beam, contrast is enhanced and ambiguities from multiple reflections are more easily resolved. A line sensor aligned to the area where the expected image of the narrow beam will fall optimally satisfies these requirements. The cost of line sensors are high, however, and it is preferred to use a lower cost TV sensor. This is particularly true when the light beam is scanned to increase the amount of measured data, for then the reflected image must be synchronously scanned to remain focused on the line sensor--a requirement that is not needed when an area sensing TV camera is used. The TV camera, however, suffers from its long integration period relative to the short time the image of the projected light beam dwells on any one part of the sensing surface.